33,606 research outputs found
Features of nucleation and evolution of defect structure in vanadium under constrained deformation
Atomic mechanisms of structural transformations leading to fragmentation in vanadium under deformation in constrained conditions without changing its volume are investigated on the basis of the molecular dynamics method. The process of formation of a fragmented structure in a deformed specimen can be divided into two stages. At the first stage, twins nucleate and grow in the crystallite. In the second stage, the orientation of lattice in twins may change due to the intersection of twins leading to their anisotropic deformation. In this case, the directions of stretching and compression of the crystal lattice in the deformed twin quite closely lie in the directions of stretching and compression of the whole crystallite
Observability of quality features of sheet metal parts based on metamodels
Deep drawn sheet metal parts are increasingly designed to the feasibility limit, thus achieving a robust process is often challenging. The fluctuation of process and material properties often leads to robustness problems. Especially skid impact lines can cause visible changes of the surface fine structure even after painting. Numerical simulations are used to detect critical regions and the influences on the skid impact lines. To enhance the agreement with the real process conditions, the measured material data and the force distribution are taken into account. The simulation metamodel contains the virtual knowledge of a particular forming process, which is determined based on a series of finite element simulations with variable input parameters. Based on these metamodels, innovative process windows can be displayed to determine the influences on the critical regions and on skid impact lines. By measuring the draw-in of the part, sensor positions can be identified. Each sensor observes the accordant quality criterion and is hence able to quantify potential splits, insufficient stretching, wrinkles or skid impact lines. Furthermore the virtual draw-in sensors and quality criteria are particularly useful for the assessment of the process observation of a subsequent process control
A Vortex Method for Bi-phasic Fluids Interacting with Rigid Bodies
We present an accurate Lagrangian method based on vortex particles,
level-sets, and immersed boundary methods, for animating the interplay between
two fluids and rigid solids. We show that a vortex method is a good choice for
simulating bi-phase flow, such as liquid and gas, with a good level of realism.
Vortex particles are localized at the interfaces between the two fluids and
within the regions of high turbulence. We gain local precision and efficiency
from the stable advection permitted by the vorticity formulation. Moreover, our
numerical method straightforwardly solves the two-way coupling problem between
the fluids and animated rigid solids. This new approach is validated through
numerical comparisons with reference experiments from the computational fluid
community. We also show that the visually appealing results obtained in the CG
community can be reproduced with increased efficiency and an easier
implementation
Enduring Lagrangian coherence of a Loop Current ring assessed using independent observations
Ocean flows are routinely inferred from low-resolution satellite altimetry
measurements of sea surface height assuming a geostrophic balance. Recent
nonlinear dynamical systems techniques have revealed that surface currents
derived from altimetry can support mesoscale eddies with material boundaries
that do not filament for many months, thereby representing effective transport
mechanisms. However, the long-range Lagrangian coherence assessed for mesoscale
eddy boundaries detected from altimetry is constrained by the impossibility of
current altimeters to resolve ageostrophic submesoscale motions. These may act
to prevent Lagrangian coherence from manifesting in the rigorous form described
by the nonlinear dynamical systems theories. Here we use a combination of
satellite ocean color and surface drifter trajectory data, rarely available
simultaneously over an extended period of time, to provide observational
evidence for the enduring Lagrangian coherence of a Loop Current ring detected
from altimetry. We also seek indications of this behavior in the flow produced
by a data-assimilative system which demonstrated ability to reproduce observed
relative dispersion statistics down into the marginally submesoscale range.
However, the simulated flow, total surface and subsurface or subsampled
emulating altimetry, is not found to support the long-lasting Lagrangian
coherence that characterizes the observed ring. This highlights the importance
of the Lagrangian metrics produced by the nonlinear dynamical systems tools
employed here in assessing model performance.Comment: In press in nature.com/Scientific Report
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